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After having compiler issues using the new PIC18F25K50 chip, I switched to the K22 series. Specifically the 28 pin PIC18F26K22. The dual USART, dual SPI/I2C interfaces will be handy and allow for more flexible board layouts.

But, I had some difficulty getting the serial output to work. I read through a variety of examples, and questions/problems posted by others, most without responses. I did find several examples, but none of these worked. With some additional messing about, I managed to come up with this minimal Hello World example.

I have been using HiTech-C with great success on the PIC16F series chips. So, when I moved to the 18F series, I tried to stick with it. But, I hit a few problems…

The new PIC18F25K50 chips aren’t supported at all.

So, I tried the supported PIC18F26K22… Some things do work, but the string libraries don’t seem to work… so, might as well just ditch this, as the PIC18 version of the compiler hasn’t been updated for a long time, I expect that Microchip may be abandoning this in favor of their new C18 compiler.

After using the 16F series and some of the simpler 18F devices, I picked up some of the PIC18F25K50 microcontrollers.

I found that the HiTech-C compiler doesn’t support the K50 series at all, so I switched over to the C18 compiler. I can get the code to compile in C18, but it won’t link. It turns out that Microchip messedup the toolchain and didn’t include the necessary libs in version 3.45.

The only thing to do is pack up those chips and wait another 6–18 months for Microchip to pull their thumb out.

The lights weren’t working on a 400 ft. radio tower. The controller’s enclosure was damaged and water had gotten in.

The board had a fair amount of corrosion, and also some scorch marks.

It looks like there may have been some transients from lightning, as the leads to one of the MOVs has melted.

I toned out the connections, and it matches the typical NE555 oscillation circuit. The damage was mostly limited to the MOVs (150L20), and the TVS protection diode (1N6281C). But, before the TVS blew, it took out a couple of traces on the board. So,I just bodged in a couple of wires to repair the trace, and it’s all running again.

This is a dual output 5V and 3.3V power supply, that operates from a 12 – 24VDC input. The intended use is for powering a special networking switch from a batterybacked supply. The device will need to operate in amient outdoor temperatures in the the central plains. Requirements:

Input: 10.8 – 26 VDC, with +/– 2V fluctuation

Output 1: 5VDC at 1.5 amps

Output 2: 3.3VDC at 5.0 amps

Output ripple < 40mv p-p

Temperature operating range (-40 to +60 degrees C.)

High efficiency

Design is based upon the LM2673 5 volt and LM22679 3.3 Volt SMPS chips. These simplify the circuit and cut the number of external components required.

The circuit is very sensitive to layout. You can breadboard this, and it might run, but the output will be very noisy and may not deliver much current. This really does need careful layout on the PC board, with care to keep the boost capacitor close to the chip, and the diode close to the inductor.

In the initial build, the 3.3V output has high noise (50mV p-p) and poor efficiency. Redesigned the layout and changed to a better diode: MBR745 from Vishay. The new layout only has 30mV peak-to-peak noise.

Shown here with out the copper pours, etc. The ICs and diodes are positioned with room to fit the heatsinks. This version runs the network switch quite well. The heatsinks do get warm, we’ll see how it performs outside on a hot day.

Problem:Multiple bench meters, scopes, etc. that connect to a workstation through a USB hub. Not all of the bench devices are optically isolated from the USB bus, so it is possible to get undesirable (and possibly damaging) ground loops through the equipment.Solution:While there are commercial USB hubs that provide isolation, they are rather expensive… typically starting around $350 for only a few ports. It seems that one should be able to build something like this for much less.One might think that it’s just a matter of splicing a couple of opto-isolators into the data wires, it’s much more complex, as shown here.There are some useful chips on the market with fairly simple application notes.This design will be based on the Analog Devices iCoupler ADuM3160 that supports both high and low speed USB, it may also supply peripheral power using an ACuM5000 chip.We’ll keep the initial version simple and skip the common-mode chokes, and leave out any diode networks for ESD protection.

Based on this chipset, I should be able to provide isolated USB ports for $10 – $15 per port.